Final answer:
The main consideration when deciding on boundary extension is the impact on the physical boundaries of our planet, including the environment and sustainability. It is important to evaluate the fraction of the planet that should be protected to ensure long-term survival and preserve a rich world for future generations.
Step-by-step explanation:
The main consideration that should always be at the forefront when deciding whether or not to engage in a boundary extension is the impact on the physical boundaries of our planet. This encompasses factors such as the environment, resources, and sustainability. We need to carefully evaluate the fraction of the planet that should be protected from human extraction to ensure long-term survival. If it is determined that half of the planet needs to be safeguarded, it may present practical and logistical challenges, but it is essential for preserving a rich world in a pristine state for future generations.